1. Field of the Invention
This invention relates to an apparatus and a method for producing monomolecular films or monomolecular built-up films generally called Langmuir-Blodgett films (hereinafter referred to as "LB films").
2. Description of the Related Art
In an LB film producing apparatus, a monomolecular film spread over a water surface is adjusted to a fixed surface pressure. A clean plate of glass or metal is raised and lowered vertically with respect to the monomolecular film so as to transfer the monomolecular film on the surface of the water, which is under the fixed surface pressure, onto the surface of the plate, thereby forming a monomolecular built-up film. In such an apparatus, a means for two-dimensionally compressing or expanding the monomolecular film on the surface of water is indispensable. Conventionally, the following two methods have been employed for such compressing or expanding (see "Langmuir-Blodgett Films" published by G. G. Roberts, Plenum Press, New York, 1990, pp. 100-105).
As schematically shown in FIGS. 1A and 1B, according to one of the methods, a trough 1 is filled to the brim with water 2 (hereinafter referred to as "subphase"). The surface 11 of the subphase is divided by one or a plurality of barriers 3, which slide along the brim of the trough, thereby varying the surface pressure of a monomolecular film 4 on the surface of the subphase.
FIGS. 2A and 2B schematically show the other method, according to which some region of the surface 11 of the subphase in the trough 1 is enclosed by a barrier band 6 and, by varying the configuration of the region enclosed by the barrier band, the area of the region is varied, thereby varying the surface tension of a monomolecular film 4 formed in that region.
However, the above-described prior-art techniques have the following problems:
In the first, simplest method, the monomolecular film 4 may escape through the gap 5 between the barrier 3 and the top of the trough when moving the barrier 3 along the top of the trough. Alternatively, due to the variation in surface tension caused by the increase in surface tension, the surface level of the subphase may be changed, thereby causing the molecules forming the monomolecular film to overflow beyond the top of the trough.
With the second method, it is possible to substantially reduce the escape to the exterior of the trough of the molecules forming the monomolecular film. In this method, a plurality of supports 7 are provided within the trough 1, as shown in FIGS. 2A, 2B and 3, for the purpose of keeping the barrier band 6 in a fixed configuration or precisely changing the area of the region enclosed by the barrier band 6. By varying the positions of some of the supports 7, it is possible to vary the area of the region enclosed by the barrier band 6, thereby varying the surface pressure of the monomolecular film 4 existing within the enclosed region. The positions of the supports 7 can be changed, for example, by attaching them to appropriate support arms 8 attached to a moveable arm 21 that is capable of making an in-plane movement parallel to the surface of the subphase. The movement of the moveable arm 21 is effected by a horizontal movement mechanism 22 utilizing a stepping motor or a DC motor. In this process, however, the barrier band 6 is caused to slide on the supports 7, with the result that part of the monomolecular film 4 is collapsed in the vicinity of the supports 7. The LB film which has been formed includes portions collapsed in this way, resulting in a deterioration in the quality of the LB film when completed.
FIG. 3 is an enlarged view showing the portion around one of the supports 7. As shown in FIG. 3, this arrangement allows part of the film material to get into the gap between the barrier band 6 and the support 7. Thus, this method has another problem in that it requires a great deal of time and labor to completely remove the film material from the barrier band when cleaning the apparatus.